The present invention relates to a method for forming fine patterns for semiconductor devices; and, more particularly, to a method for preventing the collapse of the fine patterns during subsequent processing for example a dry-etching process.
Generally, the ability to form fine patterns for highly integrated circuits is essential to the manufacture of semiconductor devices. In particular, the ability to form a fine and stable photoresist pattern is critical to the successful implementation of a semiconductor manufacturing process. As the level of integration increases, particularly for semiconductor memory devices having a high capacity of 1 Gbit or more are fabricated, the likelihood of increased levels of photoresist pattern disruption should be considered for possible effects on the device yield.
Typically, the disruption of a photoresist pattern results from one of two causes. In the first instance, the photoresist patterns peel off the substrate as a result of poor adhesion between the semiconductor substrate and the photoresist patterns. In the second instance, the photoresist patterns themselves do not possess sufficient structural stability and tend to fall, bend or break, thereby causing pattern defects that require rework or result in device failure. The collapse of the photoresist patterns is frequently thought to be related to the increases in aspect ratio required to achieve the desired level of integration of semiconductor devices. This higher aspect ratio results in tall, narrow photoresist patterns separated by narrow spaces.
The conventional wet development process includes the steps of treating the photoresist patterns using a developer; cleaning the wafer; and drying the wafer using a spin dry method. The photoresist patterns, particularly those with high aspect ratios, may collapse during the wet development process, especially during the spin dry process. In the spin dry process, the abrupt vaporization of the deionized water induces an attraction between adjacent photoresist patterns. Accordingly, if the photoresist patterns do not have sufficient strength to resist this attraction, the photoresist patterns may easily collapse. Typically, this attraction is in proportion to the surface tension of the deionized water and the aspect ratio of the photoresist patterns is in inverse proportion to a radius of a curved surface of the deionized water.
The dry development process is superior in allowing photoresist patterns having high aspect ratios to be processed without the pattern collapse that would result from a wet development process. However, as the aspect ratio increases, the likelihood of fine photoresist patterns collapsing or bending tends to increase even with a dry development process. In particular, photoresist patterns from a dry development process tend to be more prone to bending than collapsing. It is suspected that this tendency for dry-developed photoresist patterns to bend may be the result of moisture from the air cohering to the surface of the photoresist patterns.
Although the dry development process is superior to the wet development process in preventing the photoresist patterns from collapsing, the conventional dry development process still experiences problems with bending photoresist patterns as a result of moisture from the air cohering on the pattern surface.
It is, therefore, an object of the present invention to provide a method for forming fine patterns of photoresist film using a dry development process that more effectively resists a bending of the photoresist patterns.
It is another object of the present invention to provide a method for preventing moisture from cohering to photoresist patterns formed with a dry development process and then improving the reappearance of the resulting photoresist patterns.
In accordance with an aspect of the present invention, there is provided a method for forming fine, high aspect ratio patterns in semiconductor device, the method comprising the steps of: a) forming photoresist patterns using a first dry development process; and b) forming passivation layers on the sidewalls of the first photoresist patterns with a second dry development process using a fluorine-based gas, wherein the passivation layers are hydrophobic SiOx layers that prevent moisture from the air from cohering to the photoresist patterns when the semiconductor substrate is exposed to the air.
In the present invention, the first dry development process comprises the steps of: a1) forming a photoresist film for top surface imaging on a film to be patterned; a2) performing a first bake process to the photoresist film to remove solvent contained in the photoresist film; a3) selectively esposing photoresist film using a photomask; a4) performing a second bake process to the photoresist film; a5) forming silylation layers on the exposed surfaces of the photoresist film using a silylation agent; and a5) etching the photoresist film using the silylation layers as an etching mask.